A known automatic transmission device for a vehicle that can be provided with nine forward speeds and one reverse speed is disclosed in U.S. Pat. No. 7,364,527B (hereinafter referred to as Patent reference 1). For example, the automatic transmission device for the vehicle disclosed in Patent reference 1 includes four planetary gear mechanisms and six engaging elements. The automatic transmission device for the vehicle establishes nine forward speeds and one reverse speed by engaging two engaging elements of the six engaging elements.
According to the automatic transmission device for the vehicle disclosed in Patent reference 1, a sun gear of a first planetary gear mechanism is connected to an input shaft, and is selectively engaged with a carrier of a third planetary gear mechanism by a second clutch. A carrier of the first planetary gear mechanism is connected to a carrier of a second planetary gear mechanism and to a ring gear of the third planetary gear mechanism. The ring gear of the first planetary gear mechanism is connected to a sun gear of the second planetary gear mechanism, and is selectively fixed to a fixing member by a first brake. A ring gear of the second planetary gear mechanism is selectively fixed to the fixing member by a fourth brake. A sun gear of the third planetary gear mechanism is connected to a sun gear of a fourth planetary gear mechanism and is selectively engaged to the input shaft by a first clutch. A carrier of the third planetary gear mechanism is connected to a ring gear of the fourth planetary gear mechanism. The ring gear of the third planetary gear mechanism is selectively fixed to the fixing member by a second brake. The ring gear of the fourth planetary gear mechanism is selectively fixed to the fixing member by a third brake. A carrier of the fourth planetary gear mechanism is connected to an output shaft.
As such, according to the known automatic transmission device, the six engaging elements include two clutches that are the first clutch and the second clutch, and four brakes that are the first brake, the second brake, the third brake, and the fourth brake. The gear stages including nine forward speeds and one reverse speed are established by the engagement of two engaging elements of the six engaging elements. It is known that a housing does not rotate in a released state of the brake, and that the rotation of the housing in the released state of the brake is smaller than the rotation of the housing in the released state of the clutch. Thus, according to the known automatic transmission device, because the housing in the released state of the brake does not rotate, drag resistance at the engaging elements increases, comparing to drag resistance at the housing in the released state of the clutch. This is because the four brakes in which oil is easily retained within the housings of the brakes and drag resistance increases are provided, and because two brakes are released in a first gear stage when the vehicle runs forward, and three brakes are released in the second to ninth gear stages. Moreover, according to the known automatic transmission device, because two engaging elements of six engaging elements are engaged and other four engaging elements are released to have nine forward speeds and one reverse speed and the number of engaging elements released increases, drag resistance at the engaging elements increases. As such, because drag resistance increases, the transmission efficiency of the automatic transmission device may be prevented from being enhanced.
A need thus exists for an automatic transmission device for a vehicle which is not susceptible to the drawback mentioned above